V O L U M E 24, NO. 3, M A R C H 1 9 5 2 Table V.
515
Oxidative Titration of Various Monomers
Compound Methyl acrylate
Structure HzC=CHCOOCHa
Styrene
H z C = C H __ - a
Acrylonitrile
H&=CHC S
4-Vinylcyclohexene
HzC=CH
-
Remarks Sharp end point. Cooling necessary to i m v e n t loss Sharp end point. Reproducible results with cooling. Limited solubilitv Sharp end point. Linear plot. Soluble Insoluble
Solubility may prove to be a determining factor in extending oxidative titration to other compounds. Of the compounds examined, styrene, methyl acrylate, and acrylonitrile could be reproducibly determined by this new titration procedure. Figure 3 shows the linear plots obtained for each of these compounds. In order to obtain reproducible results with styrene and methyl acrylate it was necessary to cool the sulfuric-periodic acid solution in an ice bath prior to addition of the sample. Eventually it is hoped to investigate other compounds that may be subject to oxidative titration. This method may be applicable to the problem of measuring unsaturation in a number of aliphatic compounds, providing a satisfactory water-soluble 601vent can be found for both the reagents and sample. The reactions occurring during oxidative titration are being investigated. ACKNOWLEDGME3T
methacrylate rod stock, in order to determine the uniformity of monomer distribution throughout such a large cross section. Fractionation of the rod was accomplished by removing successive layers on a lathe. This operation was performed slowly to minimize heat effects and consequent polymer degradation. Table I V shows the data obtained from this experiment. -41~0 included are data from several cast sheeting samples from which successive l/lG-inchlayers were obtained by milling. Oxidative Titration of Other Monomers. A number of compounds were subjected to oxidative titration as in the recommended procedure. Each of the compounds examined contained one or more terminal methylene groups as shown in Table V. Pertinent remarks concerning the behavior of these compounds on oxidative titration are also included. The compounds listed in Table V as giving sharp end points are those in which the terminal carbon-to-carbon double bond is conjugated with a strongly polar group such as carbalkoxyl, cyano, or aryl. These compounds are also soluble in the reaction medium.
The authors wish to acknowledge the helpful contributions to this paper made by A4nneGreco of this laboratory. The authord appreciation of statistical methods resulted from the combined efforts of W. L. Gore and Mary T. Dunleavy. LITERATURE CITED
(1) dssoc. Offic. Agr. Chemists, “Official a n d T e n t a t i v e Methods of Analysis,” 6th ed., p. 495, 1945. ( 2 ) Bricker, C. E., a n d Johnson, H. R.. ISD. ESG. CHEM.,ANAL.ED., 17, 400 (1945). (3) Bricker, C. E., a n d R o b e r t s , K. H., AXAX,.CHEM.,21, 1331 (1949). (4) Dunlop, E. C., “ Q u a n t i t a t i v e Analysis b y M e a n s of Catalytic Hydrogenation Reactions,” paper presented before Kew York rlcademy of Sciences, M a r c h 25 a n d 26, 1949. (5) M a r q u a r d t , R. P., a n d Luce, E. N., AXAL. CHEhz., 21, 1194 (1949). (6) Whitmore. F. C., “Organic C o m p o u n d s of Mercury,” p. 37, New Y-ork, Chemical Catalog Co., 1921.
R E C E I V E for D review
.luglist ’25, 11351.
Accepted Kovember 8, 1951.
Estimation of Guanidine with Calcium Picrate PERCY FAINER AND J. L. MYERS Analytical Section, Canadian Armament Research and Dezelopment Establishment, Valcartier, Qtiebec, Canada A rapid procedure for the routine estimation of guanidine in the presence of large amounts of impurities was required. The usual picrate procedures were critically dependent on experimental conditions and unsatisfactory in the presence of foreign salts. Comparisons of the calcium picrate and the usual ammonium picrate methods have shown that the former is more rapid and less dependent on experimental conditions, gives better precision (within
G
C A N D I N E is usually determined gravimetrically as the picrate, using ammonium picrate as the precipitating agent. The procedures generally employed are variations of the Vozarik method for guanidine ( 5 ) . I n this establishment the method of Smith et al. n-as originally used for the estimation of guanidine. The reagent consisted of an aqueous saturated solution of ammonium picrate saturated with guanidine picrate (250 ml. per determination) to decrease the solubility of guanidine picrate. The most recent method used by the authors is that described by the American Cyanamid Co. (1). Correction for solubility of guanidine picrate is achieved by means of a curve based on results obtained using a carefully standardized procedure. In agreement with Dodd (3) it was found that any method for
(e)
0.1% even in the presence of 50% impurities), and is slightly more accurate. The calcium picrate method is ideally suited for the routine estimation of guanidine in crude products. Calcium picrate is’ about 20 times more soluble than ammonium picrate, a fact that is of advantage in several ways. The use of the chelating agent, Versene, to prevent interference by the calcium ion in the presence of sulfate impurities is noteworthy. the estimation of guanidine using ammonium picrate as the precipitating reagent is critically dependent on the conditions of the analysis. Variations in pH, weight of sample, time and temperature of standing of precipitate before filtration, and method of precipitation all have a deleterious effect on the precision and accuracy. These methods have been found unsatisfactory for the routine analysis of large numbers of samples because of the length of time required per determination, and the lack of precision and accuracy obtained in the presence of foreign salts. It is clear that a smaller volume of precipitating reagent containing a greater concentration of picrate ion would eliminate many of the errors inherent in methods employing ammonium picrate, most important of which is the solubility of guanidine picrate. I n this laboratory it has been found that calcium picrate
CHEMISTRY
ANALYTICAL Table I.
Effect of Varying Conditione
(Using 3% calcium picrate.
Conditions Varying pH
Results are average of three determinations) Guanidine Guanidine Picrate Nitrate % Mean ReTaken, covered, ReDeGram Grams covery viation
DISCUSSION
2.3 5.0 6.5 9.5 11.8
0,5000
1.176 1.174 1,174 1.174 1.181
99.7 99.5 99.5 99.5 100.1
0.10 0.10 0.03 0.07 0.10
0.5000
1.169 1.174 1.174
99.1 99.5 99.5
0.03 0.03 0.03
0,5000 0.5000 0.5000 0.5000
1,174 1.175 1.173 1.174
99.5 99.6 99.4 99.5
0.00 0.07 0.03
0..5000 0.5000
1.174 1.174
99.5 99.5
0.03
0,5000 0.5000 0.5000 0,5000
Effect of Varying Conditions. The following conditions were examined, using 3% calcium picrate: pH, method of precipitation, time of standing, and temperature of standing. It will be seen from Table I that the calcium picrate procedure is not critically dependent on experimental conditions.
Varying time of standing before filtration, hours 0.5000 0.~000
1
2 17
Varying temperature of standing before filtration, OC. 20 25 30
reagent, as sodium picrate will precipitate. The following procedure was adopted: Five milliliters of Versene were added to an aliquot of the standard guanidine nitrate solution. The solution was then heated to boiling and 50 ml. of hot calcium icrate solution were added. The remainder of the procedure is ifentical with the general procedure.
General procedure H o t reagent added t o hot soliition of sample Cold reagent added t o sample
Table TI.
0.08
Effect of Varying Weight of Sample
(Results are average of three determinations) Guanidine Guanidine Nitrate Picrate % Taken, Recovered, ReReagent Gram Grams covery 0.2235 0.0997 3'5 calcium picrate 94.9
0.07
is ideally suited for this purpose, as it is extremely soluble in water (about 30% a t 25' C.), Numerous experiments were carried out to determine the suitability of this reagent for use in determining guanidine under various experimental conditions.
4 % calcium picrate
MATERIALS
430% stock solution of calcium picrate was prepared by boiling 280 grams of picric acid and 150 grams of calcium carbonate with 500 ml. of water until the evolution of carbon dioxide ceased. The solution was cooled, filtered, and diluted to 1 liter. The resulting solution was standardized by determining the picrate gravimetrically as nitron picrate (2). The various concentrations of calcium picrate used in the work were made up by diluting the 30y0stock solution to the requlred volume. Saturated aqueous guanidine icrate was used as wash solution. -4standard solution of guaniine nitrate (0.5 gram per 10 ml.) was prepared from guanidine nitrate which had been recrystallized twice from water and once from alcohol. The tetrasodium salt of ethylenediaminetetraaceticacid (Versene) was used as a liquid 34% solution (Bersworth Chemical Co., Framingham, Mass.). Gooch crucibles, size 3. Filter paper mats,& & S. S o . 895 E, 21 mm. EXPERIMENTAL
General Procedure. An aliauot of the standard guanidine nitrate solution (not more than 15 ml.) was pipetted into a 150-ml. beaker, 50 ml. 101 of hot (95' C.) calcium picrate solution were added, and the solution plus precipitate was allowed to stand for 2 hours at room temperature (except where otherwise specified). The precipitate was filtered by means of suction, 99 using a tared Gooch crucible fitted with a filter paper mat, washed with the guanidine picrate wash solution, dried a t 110' C. for 1 08 hour, cooled in a desiccator, and weighed. Care was taken to draw off by suction any excess solution from the precipitate and to 97 remove with filter paper any excess drops of filtrate adhering to the bottom of the crucible. minations were carried out in the presence of impurities, these were added to the sample before addition of calcium picrate. Unless otherwise stated, all determinations were carried out a t the pH of the reagent. Variations in pH were obtained by the addi-
2
95
94
93
¶e
I
0.3444 0.5823 0.8225 1,170 1.730 1.855 0.2360 0.3435 0,5887 0.8250 1.175 1.411 1.762 1,998 0.2350 0.5930 0.8302 1.184 1.422 1.772 2.010
0.1493 0.2490 0.3488 0.4990 0.7480 0 8478 0.1000 0.1482 0.2490 0.3488 0.4990 0.5986 0.7480 0 8478 0.1000 0.2493 0.3494 0 4995 0.5990 0.7490 0 8490
5% calcium picrate
Nean Deviation 0.3 0.10 0.08 0.07 0.02 0.20 0.25 0.42 0.13 0.13 0.00 0.07 0.10 0.03 0.10 0.03 0.20 0.13 0.17 0.10 0.03 0.00
97.8 99.1 99.9 99.3 98.0 92.7 97.8 98,5 100.1 100.1 99.8 99.9 99.8 99.9 99.8 100.9 100.9 100.5 100.7 100.5 100.5
Reliable results were obtained over a pH range of 5.0 to 9.5. Beyond these limits a positive error is apparently introduced. Unlike the ammonium picrate procedure, long periods of standing are unnecessary for complete precipitation. Quantitative results are obtained with only 2 hours' standing. Moreover, the use of a constant temperature bath is unnecessary, as identical results were obtained over a temperature range of 20' to 30' C. The use of hot reagent as described in the general procedure is unnecessary as far as accuracy and precision are concerried, but it aids in obtaining well defined crystals capable of easy filtration.
I
,
,
1 I
1
1
,
j
I I
l
l
I 21
V O L U M E 24, NO. 3, M A R C H 1 9 5 2
517
I t is recommended that the method outlined in the general procedure be used wherever possible. Effect of Varying Weight of Sample and Concentration of Reagent. Determinations were carried out with samples of different weights, using 3, 4, and 5% calcium picrate. As shown i n Table 11, 4% calcium pitrate gives the best results when the precipitated guanidine picrate is within the range of 0.59 to 2.0 grains.
addition of the calcium picrate. Versene chelates with calcium to form a very stable soluble complex, thus preventing the precipitation of insoluble calcium salts. Although Versene is basic, i t does not interfere, as the pH of the resulting solution is less than 9.5. Melamine impurities in concentration high enough to saturate the aqueous sample solution (15 ml.) did not interfere, providing the p H of the solution was not less than that of the calcium picrate reagent.
Table 111. Effect of Impurities
CONCLUSION
(Esing 4% calcium picrate.
Impurity, Inipurities Gram S o impurity added 0 . 5 Ammonium nitrate 0 . 5 Ammonium sulfate and 5 ml. of Versene Melamine Urea
0.5
0.5
0.045 0.5
Results are average of three determinations) GuaniGuanidine dine Picrate Nitrate Re% Mean Taken, covered, ReDeviaGram Grams covery tion 0.4955 0.4955 0.2995
0 5840
100.1 99.9 99.9
0.03 0.00 0.07
0.4985 0.4985 0.4955
1 168 1 168 1 168
99.9 99.9 99.9
0.10 0.13
1.17
1.168
0.03
Figure 1, which reflects graphically the results given in Table 11, shows that, with increasing concentrations of calcium picrate, higher results will be obtained, probably because of increased adsorption of calcium picrate. It is recommended that a 4'% solution of calcium picrate, adjusted to within &O.l%, be used for the analysis of samples containing between 0.25 and 0.85 gram of guanidine nitrate. Further work is planned to develop a procedure for samples containing smaller quantities of guanidine nitrate. Effect of Impurities. The effect of impurities was tested a t the p H of the reagent, using 4% calcium picrate. Ammonium nitrate, ammonium sulfate, and urea in amounts up to.0.5 gram per 50 ml. of calcium picrate had no adverse effect on the determination (see Table 111). In one instance an experimental sample containing about 70y0 ammonium nitrate was determined satisfactorily by taking a weight of sample such that the weight of ammonium nitrate did not exceed 0.5 gram. The weight of guanidine nitrate in the sample was within the prescribed limits. In the presence of ammonium sulfate, calcium sulfate was prevented from precipitating by adding Versene to the sample before
In the estimation of guanidine as the picrate, calcium picrate was found to be a more satisfactory precipitating reagent than ammonium picrate. Interference by impurities normally found in guanidine nitrate is not critical when the calcium picrate reagent is employed. In the presence of large amounts of urea, ammonium salts, or melamine, no noticeable error is introduced. In contrast to ammonium picrate reagents, it is unnecessary to p r e pare large volumes of solution. because of the extremely high solubility of calcium picrate. Experimental results show that when aqueous calcium picrate is used, the procedure is faster and less dependent on experimental conditions. The method has been found to be ideal for control analysis. Between 30 and 40 samplee a day can readily be determined by an average operator, Fith satisfactory precision and accuracy. The precipitation of ions forming insoluble salts with calcium can be eliminated by the use of Versene, which chelates with calcium to form a stable soluble complex. I n most experiments conducted with calcium picrate, the average deviation of the results is less than 0.1%. Even in the presence of large amounts of impurities the accuracy is unaltered. N o correction factor need be employed if the weight of guanidine picrate recovered is within the range 0.5 to 2.0 grams. LITERATURE CITED
(1) -4merican Cyanamid Co., "Cyanamid's Nitrogen Chemicals Digest, The Chemistry of Guanidine," Vol. IV, p. 37,1950. (2) Busche, M., and Blume, G., 2.angew. Chem., 21,354(1908). (3) Dodd, A. H., J. SOC.Chem. Znd., 41,145T (1922). (4) Smith, Sabetta, and Steinbach, Ind. Eng. Chem., 23, 1124 (1931). (5) Voaarik, Z.angew. Chem., 15,670 (1902). RECEIVED for review March 15, 1951.
Accepted October 18, 1951.
Refractive Index-Temperature Data for Anhydrous Ethyl Alcohol THOMAS E. SMITH AND ROBERT F. BONNER U . S. Industrial Chemicals, Znc., Baltimore 3, M d .
A
LTHOUGH eome of the physical properties of ethyl alcohol are well established-e.g., density and boiling point-the published refractive index-temperature data on this compound show extreme disagreement. Consequently, a pure sample of anhydrous ethyl alcohol was prepared and its refractive index carefully determined between 10' and 30' C. PURIFICATION O F ETHYL ALCOHOL
The absolute alcohol obtained for this work was tested for the following impurities: methanol, isopropyl alcohol, tert-butyl alcohol, amyl alcohols, aldehydes, ketones, acids, benzene,, water, and nonvolatile matter. The only appreciable quantity of impurity present was 0.25% by weight of n-ater; con-
sequently, the sample was agitated overnight with anhydrous calcium sulfate and allowed to stand over this drying agent for 3 days with a drying tube attached to the flask to prevent the introduction of moisture from the atmosphere. The alcohol was then distilled in a dry nitrogen atmosphere. The fraction used for the refractive index determinations had a constant boiling point of 78.32' C. a t 760 mm. and contained 0.03 weight % water. The effect of this amount of water on the refractive index of ethyl alcohol (ea. 0.00001 unit) is within the accuracy of the refractometric method used. DETERMINATION O F REFRACTIVE INDEX-TEMPERATURE DATA
The refractive index readings were made a t 5 O intervals between 10' and 30" C. using a Bausch & Lomb dipping refractometer
